CAL-collaborative organic research and extension network: on-farm research to improve strawberry/ vegetable rotation systems in coastal California

CAL-CORE is a network of researchers, farmers, extension professionals, industry and non-profit organizations dedicated to furthering research into organic strawberry and vegetable production in coastal California. Formed 9 years ago, we have worked on a variety of fertility, pest and disease management issues facing organic growers. Currently, our main effort centers on vegetable/strawberry rotations and different options for fertility and disease management. In a replicated field trial we compare treatments across a range of sustainability criteria: crop yield, nitrogen cycling and losses, greenhouse gas emissions, disease incidence, biocontrol of insect pests, soil carbon pools, and economics. Main treatments are 2 versus 4 year rotations with different crop combinations believed to be either suppressive of a major soil borne disease (Verticillium wilt), or more profitable but more conducive to disease. Superimposed on the rotations are fertility treatments (legume/cereal cover crop only, legume/cereal cover crop + compost + additional fertility amendments, cereal cover crop + mustard seed meal, or untreated control) and in the two legume/cereal cover cropped treatments anaerobic soil disinfestation (ASD, a promising option for controlling a range of soil borne diseases) is used for disease management prior to planting strawberries. Six network farmers also chose a sub-set of these treatments to test on their farms and compare to their own management practices. The study is in year 4 and all treatments at all locations are now planted to strawberries. Preliminary data show Verticillium wilt to be the major cause of yield loss in strawberry, and that ASD provided partial control, but mustard seed meal did not. Soil inorganic N pools are very dynamic with rapid release of nitrate from crop residues observed. Soil carbon is already declining in the bare fallow (no winter cover crop) treatment and in the 2 year rotation as compared to the 4 year rotation. This project will provide farmers with tools to improve their production systems, meet water quality regulations, and quantify climate-related impacts of these intensive organic systems.